Probably most important part of e-mail security is to make sure you do not cripple yourself. Its more than just adding proper passwords to you POP3 of IMAP accounts.
1. Make sure you do not select the wrong recipient by turning off the automatic addressing features. A good example of where this could go wrong is with Microsoft Outlooks automatic filling feature. This could be very problematic when sending confidental of private e-mails.
2. Try and use BCC when sending to more than 1 recipient. It is always bad to share e-mail addresses, not to mention that not everyone want their e-mail address to spread the whole world. Every time you send e-mails with all the e-mail addresses in the To or CC field you are sharing those addresses with all the people you mail.
3. Save e-mails in a secure place. No amount of security is sufficient if, after you receive your e-mails, you store them in a location where everyone can find them.
4. Use Private Accounts for Private e-mails. Every mail you share with the world is likely to be targeted by spammers and phishers. The more spammers and phishers use your address, the more likely it is for you mail address to end up being marked as a spam address and being blacklisted by ISPs.
5. Double check you recipients, especially when replying to a message sent to a mailing lists. It could be a real problem when you reply and the message is accidentily sent to the whole list, instead of just the one person you ment to send it to.
These tips are more focused on users whole might “break” their own security efforts. Do not be your own worst security issue. 🙂